1. Field of the Invention
This invention relates to a cage for a ball bearing serving as a ball guide. This cage is preferably used for, for example, a ball bearing for a revolving seat which supports the rotary segment of a CT scanner.
2. Related Art
For example, in a ball bearing for a revolving seat having a large diameter, where a cage in the same type as a cylindrical cage used for a ball bearing for a general machine tool is adopted (e.g. see JP-A-2004-60775), the thickness of the cage becomes very thin relatively to the diameter thereof. Therefore, the rigidity is lowered so that the cage becomes likely to warp. Where such a cage is used, if the lead/lag of the balls occurs, the region between adjacent cage pockets of the cage may be pulled circumferentially so that the cage is elastically deformed in a straight shape; or otherwise may be contracted so that the cage is elastically deformed in a warped shape. Where such a cage is formed in a race guiding structure guided by a bearing ring member such as an outer ring and inner ring, the elastically deformed portion of the cage is likely to be brought in slidable contact with the bearing ring member. This leads to occurrence of abrasion and noise.
Incidentally, there is a general cylindrical cage circumferentially divided into a plurality of segments. In this case also, the inconvenience as described above occurs. This cage is a cylinder composed of a plurality of plate-like segments which are coupled with one another. At a plurality of positions in a longitudinal direction of each plate-like segment, cage pockets which penetrate through a radial direction are provided (for example, JP-A-2003-120680). There is also a cage in which in the inner and outer circumferential openings of all the cage pockets, lugs having the same shape for stopping the come-off of balls are provided.